The application relates generally to semiconductor processing equipment and particularly to measuring the alignment of components located within the semiconductor processing equipment and to adjusting the position of misaligned components within the semiconductor processing equipment.
Semiconductor processing equipment is used in the deposition, patterning, and treatment of thin films and coatings. A conventional semiconductor processing system contains one or more processing chambers and a means for moving a substrate between them. A substrate may be transferred between chambers by a robotic arm which can extend to pick up the substrate, retract and then extend again to position the substrate in a different destination chamber. Each chamber has a pedestal or some equivalent way of supporting the substrate for processing.
A pedestal may supply heat to a substrate during processing. Heat may be provided by a resistive mechanism to a refractory metal coil embedded in the heater plate. The substrate may be held by a mechanical, pressure differential or electrostatic means to the pedestal between when a robot arm drops off the substrate and when an arm returns to pick up the substrate. Lift pins are often used to elevate the wafer during robot operations. When on the pedestal, one or more processes may be performed. These may include annealing the substrate and depositing or etching a film on the substrate.
Most processes provide more benefit when the process uniformity across the substrate surface is higher. One of the parameters which may affect uniformity is the position of the substrate during processing. As a result, processing systems are preferably designed to provide reproducible placement of substrates during processing steps.
An illustrative example of a process and associated process chamber which can suffer from a less than optimal reproducibility in the pedestal and substrate position is epitaxial film growth (often referred to as EPI). Deposited film uniformity (e.g. film thickness and dopant density) in an EPI process, as with many other processes, can be sensitive to tilt and a lateral misalignment of the substrate. The position of the substrate is determined, in part, by the position of the pedestal.
In an EPI process, a portion of the heat supplied to the substrate may come from optical radiation sources which expose the heater plate and/or the substrate to light. This method is also desirable for rapid thermal processing and other processes which benefit from higher substrate temperatures. Substrate processing chambers designed for radiative heating usually use quartz for some portion of the chamber wall because of its ability to tolerate high temperatures, low coefficient of thermal expansion and excellent transparency to infrared and visible light. EPI chambers may employ quartz domes for the top and/or bottom of the chamber to allow the radiation to impact the substrate and pedestal. The pedestals in EPI chambers are often called susceptors because they absorb radiation and provide heat to the substrate.
These quartz domes may be relied upon for support of interior chamber components like the pedestal, which can be a susceptor. Quartz domes are shaped at high temperatures when the glass is ductile, giving rise to tolerance variabilities. FIG. 1A depicts a schematic view of an EPI chamber. The bottom quartz dome 104 is shown providing support for a shaft 108 and a rigidly affixed pedestal 112, which together may be referred to as a substrate support assembly. The pedestal is shown in FIG. 1A indicating a non-negligible misalignment with a preheat ring 116 upon assembly. The substrate support assembly is tilted about a pivot point 106 with an approximate location indicated near the bottom of the shaft.
A prior art technique for correcting this tilt (i.e. leveling the pedestal) is to apply a force against the shaft 108 above the pivot point 106 to rotate the substrate support assembly clockwise. The net result of this technique is shown in FIG. 1B. The tilt has been corrected, but a lateral offset has been introduced resulting in a non-uniform gap between the pedestal and the preheat ring. Note in this two dimensional depiction, the gap on the left 120 is larger than the gap on the right 121.
In addition to the coupling between the tilt and lateral location, the technique currently used has other drawbacks. The pedestal is adjusted using a manual process that uses a contact straight-edge leveling tool. An operator using the straight-edge may visually judge the pedestal positioning and manually adjust the tilt and/or translation mechanism of the pedestal until visually it appears adequate. The reliance on visual measurement is undesirable as it is subjective, time-consuming and prone to human errors. It also necessitates opening the chamber upper dome requiring the chamber to be vented to atmosphere which brings with it a loss in productivity due to significant down-time and recovery time.
Another drawback to the prior art technique for correcting tilt and lateral location is that the correction is done prior to pumping down the semiconductor processing apparatus. Pumping down a semiconductor processing apparatus can cause components to shift, move or even flex. Components that are aligned prior to pumping down a semiconductor processing apparatus can become unaligned after pumping down. For example, a pedestal that is aligned when the semiconductor processing apparatus is opened can become misaligned for processing conditions because the semiconductor processing apparatus is closed up and pumped down before processing. Therefore, prior art techniques for correcting tilt and lateral location have the drawback that although components can be aligned during the alignment process, those components may become misaligned before or during processing of wafers.
Therefore, a system and method is needed for independently adjusting the tilt and lateral location of a component in a semiconductor processing apparatus while the semiconductor processing system is fully assembled.